The present disclosure relates to the field of large scale integrated circuit manufacturing, and in particular to a wafer processing apparatus and method.
Both a large-scale advanced integrated circuit manufacturing and a small batch of research and development type micro-nano processing involve wet etching and cleaning process. The wet process is generally divided into three parts: chemical liquid soaking, deionized water washing, and final drying.
The main methods of drying are as follows:
1. Mechanical drying represented by SEMITOOL SRD (registered trademark)
The drying method is to throw most of water out of a wafer surface in a short time (˜5 minutes) by centrifugal force, and then dry it in the form of evaporation by hot nitrogen for a long time (˜25 minutes). Because of the mechanical rotation, the wafer will accumulate lots of static electricity, and despite the remedial measures such as Electrostatic neutralization, it will still be affected by the particles. If it is a hydrophobic surface, the particle problem can be very serious. In addition, this manner of mechanical rotation plus evaporation by blowing heat N2 is not suitable for drying many high line-width ratio structures and micro-electromechanical systems (MEMS) devices, in which the capillary force in the process of water evaporation will directly pulls weak structures thereof and cause permanent defects such as adhesions. Furthermore, since the manner involves a mechanical rotation with a center of the wafer as an axis, the centrifugal force at the central portion of the wafer is close to zero, so this drying manner is difficult to adapt to the post-hydrofluoric acid (HF-last) wafer. Because water droplets in the center part can only be dried in the hot N2 step for a long time, and a machine is not completely isolated from the outside, the residual O2 and water droplets in the machine can easily form defects called water marks on a hydrophobic surface.
2. Steam drying by replacing moisture on a surface of a wafer with an organic solvent vapor of low surface tension
A typical example is isopropyl alcohol (IPA) steam drying invented by Professor T. Ohmi and others of Waseda University, Japan. As shown in Table 1, at 25° C., the surface tension of IPA is less than ⅓ of water, so the capillary force at the time of evaporating is much smaller than water, and their boiling point is lower than water (Table 2), there is very high steam pressure, which helps evaporate for drying.
TABLE 1Surface tension of various liquids at different temperaturesMolecularγ (mN/m)formulaname10° C.25° C.50° C.75° C.100° C.Br2Bromine43.6840.9536.40H2Owater74.2371.9967.9463.5758.91H4N2hydrazine66.39Hgmercury488.55485.48480.36475.23470.11CH4OMethanol23.2322.0720.14C2H6OAlcohol23.2221.9719.89C2H6O2ethylene47.9945.7643.5441.31glycolC3H6Oacetone24.5722.7219.65C3H8Opropanol24.4823.3221.3819.43C3H8Oisopropanol22.1120.9318.6916.98
TABLE 2Boiling point of various liquids at different pressuresMo-temperature (° C.)lecular10100formulaname1 Pa10 Pa100 Pa1 kPakPakPaC3H8Oisopropanol−65e−49e−28e−1.333.682.0CH4OMethanol−87e−69e−47.5−20.415.264.2C2H6OAlcohol−73e−56e−34e−7e29.278H2Owater−60.7 s−42.2 s−20.3 s7.045.899.6C3H6OAcetone−95−81.8−62.8−35.61.355.7C3H8Opropanol−54e−38e−16e 10e47e96.9
Where e is an abbreviation for evaporation, indicating that the liquid begins to evaporate; s is an abbreviation for solid, indicating that the liquid is still in a solid state.
Although it has the advantages of high-volume drying of wafers, no static interference, low particles, etc., due to the high IPA temperature (82° C., IPA boiling point at atmospheric pressure), the safety requirements are extremely high. Because a pure evaporation mode is employed, the process time is much longer than mechanical drying, and it consumes more IPA and sometimes leaves organic residues.
3. The Marangoni principle drying method invented by Philips in the Netherlands
After the wafer is placed in the water tank, while it slowly floats out of the water, an organic solvent vapor of low surface tension, such as IPA, is fed. Because IPA and water are miscible, the concentration of IPA close to the wafer is higher than the concentration of IPA in the sink. This creates a surface tension gradient between the surface of the wafer and the sink, and the direction is from the wafer to the sink. The moisture on the surface of the wafer is gradually pulled to the sink by the Marangoni effect, so as to achieve drying effect. The Marangoni principle drying has low consumption of IPA (20˜30 mL/time), short process time (10˜20 minutes), and is accomplished at room temperature, so it has become a main drying method in the relevant field. Because the water is taken away by the physical force of the Marangoni effect, this drying method has a very perfect effect in avoiding water marks. However, the Marangoni effect can only form a surface tension gradient on a relatively smooth and hydrophilic surface, so this drying manner is difficult to apply to devices or structures that are relatively sensitive to capillary forces or of high line-width ratios, such as MEMS, TSV, and the like. Since it is only an imitation of an IPA steam dryer at that time, and it works at a room temperature, frequently, the wafer can not be completely dried. If it is a hydrophobic surface, it is also difficult to form an effective surface tension gradient and the drying mode will also become an IPA vapor drying, with the addition of the condition being normal temperature, normal pressure, and non-isolation from the outside, the wafer surface is easily oxidized by oxygen, which is easy to form water marks.
4. Supercritical drying
The last method is supercritical drying that can only be used for release in small volume MEMS manufacturing processes. This drying method bypasses critical points of the three phases of the water, directly sublimates it, avoiding problems such as adhesion caused by capillary force, and is commonly used in the manufacture of MEMS devices. However, because of the large amount of liquid CO2 used and a long process time (˜1 hour), it is not able to be used in an integrated circuit process.
As an overview of the advantages and disadvantages of the above drying machines, and in view of a trend that the morphology of integrated circuit devices develops from two-dimensional planar structure to three-dimensional structure, such as dense fin field effect transistor (Fin-FET), high line-width ratio DRAM, nanowire field effect transistor, etc., more wafers are stacked vertically in the package such as TSV, and the density of high line-width ratio (AR) deep trench structure in the wafer is getting higher and higher, so it is necessary to develop an efficient drying method that can meet the demand.